Question

rick is driving to his friend's house. The speed limit is 35 mph, but he goes 10 over. The trip takes him 20 minutes. How much longer would the trip have taken him if he drove the speed limit?

Answer 1

20 minutes is 1/3 hour.

Rick goes 45 mph for 1/3 hour so a distance of

`45 \textrm{ miles/hr} * \frac 1 3 \textrm{ hr} = 15 \textrm{ miles}`

At 35 mph that would take

`t =15 \textrm{ miles} / 35 \textrm{ mph}= 3/7 \textrm{ hrs}`

That's

`3/7 - 1/3 = 9/21 - 7/21 = 2/21 \textrm{ hrs}`

Answer: 2/21 hours

That's about 5.7 minutes longer